Square wave generator



Feb. 9, 1943. G. SWIFT 2,310,328

SQUARE WAVE GENERATOR Filed May 25, 1938 nnn TIME

lnnentor Patented Feb. 9, 1943 SQUARE WAVE GENERATOR Gilbert Swift, Philadelphia, Pa., asslgnor to Badio Corporation of America, a corporation of Delaware Application May 25, 1938, Serial No. 209,877 3 Claims. (01. 250-36 W invention relates to generators for the production of square or rectangular waves. More particularly, my invention relates to an improved neon tube oscillator which may be conveniently used to produce square or rectangular waves and which is economical by reason of its extreme simplicity.

There is a frequent need in the radio art for oscillators which are capable of producing square or rectangular waves. For example, such waves are frequently used in testing various types of amplifiers, filters, and other circuits. I am aware that many circuits have been proposed for the production of oscillatory waves answering this description. Such oscillators usually make use of a series of over-excited amplifiers or a plurality of grid control gaseous discharge tubes of the thyratron type. While both of the above mentioned methods are capable of producing oscillatory waves of the required shape, they are subject to the disadvantage of relatively high cost due either to the large number of tubes required or to the use of the thyratrons and the more complicated circuits which are required.

According to this invention, a square wave oscillator has been provided which utilizes two simple neon tubes and a single pentode or triode amplifier. The basic neon tube oscillator consists of a capacitor which is charged to a given voltage through a resistor, and a neon tube which is utilized to discharge the capacitor when the breakdown voltage of the tube has been reached. The output voltage of such an oscillator is substantially saw-tooth in shape. Consequently, it is not satisfactory for the proposed use. However, its extreme simplicity and its wide range of frequency suggests the desirability of adapting this type of oscillator to produce a square wave.

It is therefore an object of this invention to provide a neon tube oscillator whose output voltage is substantially rectangular or square.

It is a further object of this invention to provide a simplified square wave oscillator.

A further object i to provide a square wave oscillator which may be easily constructed, which is stable in operation, and which may be easily adjusted.

A still further object oithis invention is to provide an oscillator, the output voltage of which may be easily adjusted to give a rectangular wave shape throughout a wide degree of latitude.

This invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope is indicated by the appended claims. Similar reference numerals are used to indicate similar parts throughout the drawing.

Referring to the drawing,

Figure 1 is a schematic circuit of one form of neon tube oscillator according to my invention;

Figures 2, 3 and 4 represent the wave shape of various voltages which may be obtained from the circuit illustrated in Fig. 1;

Figure 5 illustrates an alternative embodiment of my invention which combines the neon oscillator with an overbiased amplifier to produce a completely rectangular wave, and

Figures 6, 7 and 8 represent various wave shapes which may be obtained by the device illustrated in Fig. 5.

Referring to Fig. 1, two resistors II and I are serially connected by a potentiometer 8. A capacitor [3 is connected between the opened ends of this resistor network. The condenser I3 is also connected to one plate of each of two neon tubes l and 3. The remaining plate of the neon tube I is connected to the negative terminal of an energizing battery I5. The remaining plate of the neon tube 315 connected through a resistor 5 to the same terminal of this battery IS. The positive terminal of the battery is connected to the movable arm 25 of the potentiometer 5. A pair of output terminals I1 and H are connected to the extremities of resistor 5.

The operation of this oscillator is as follows: Assuming that neither neon tube is conducting, voltages will be applied across both tubes from the battery 15. Because of the fact that the characteristic breakdown voltage of two neon tubes is never absolutely the same, one of them will break down before the other. When this happens, current will suddenly flow from the positive terminal of battery l5 through a portion of the potentiometer, one of the resistors I or I I and the tube which has become conductive. Assuming that neon tube I reaches its breakdown point before neon tube 3, the current through resistor ll suddenly becomes quite large. This current produces a voltage drop in resistor H and consequently the voltage at this neon tube is suddenly decreased. Capacitor [3, in response to this sudden decrease in voltage, induces a decreasing voltage on the second neon tube 3 which momentarily prevents the voltage across the second tube from reaching the breakdown point of that tube. A short time later, the voltage across capacitor l3 leaks oil through the resistors connected across its terminals. Normal potential is restored to the second neon tube 3.

Consequently, this tube now breaks down and draws a substantial current through the resistor 1. The resultant voltage drop is now transferred back to the first neon tube. It is of such a potential that the voltage across the first tube I drops below its extinguishing point. As before, the potential across the capacitor then discharges through the resistors I, 9 and II. The potential across the first neon tube rises until the breakdown point is again reached, and the process repeated. a

The output voltage is represented, for a. particular operating condition, by the curve of Fig. 2. If the voltage be measured across the output terminals l'i-i9 it willbe zero during the period at which the neon tube 3 is non-conducting. This is represented in Fig. 2 by the time interval T. When tube 3 breaks down the voltage across resistor 5 rises to a maximum. Since the charge in capacitor I3 will fiow through the neon tube 3 and the resistor 5, a slight decrease in the voltage will be noted during the interval of discharge. This interval is represented in Fig. 2 by the time interval T. When the discharge has been completed and the voltage on the first neon tube restored, the second neon tube will then be extinguished, the current through resistor 5 will drop to zero, and the out put voltage will return to zero.

By varying the position of the tap 25 on the potentiometer 9 wave shapes of the type illustrated in- Figs. 3 and 4 may be obtained. The frequency of this oscillator may be varied by changing either the applied voltage, the value of the capacitor l3, or the value of the various resistors.

It will be noted that the wave shape produced .by the device illustrated in Fig. 1 is not perfectly rectangular. While it may be sufficient for many purposes, if it is desirable to obtain a perfectly rectangular wave shape, a simple pentode or triode amplifier tube may be connected across the output. terminals in the manner shown in Fig. 5.

Referring to Fig. 5, the neon tube oscillator itself is identical with that shown in Fig. 1, and need not-be described again. The addition consists of a triode 2| whose input circuit is connected across the terminals l1;-|9. A resistor 23, which may be variable, is connected between the plate of this triode and the battery IS. The output voltage may now be taken across the resistor 23. In this application it is, of course, necessary that the voltage drop across resistor 5, when the neon tube 3 is conducting, be sufficient to bias the amplifier below its plate current cut-off point.

The operation of the oscillator section of this device is'similar to that of Fig. 1. When the neon tube 3 is conducting, the resultant voltage drop across resistor 5 biases th amplifier 2| well beyond plate current cut-off. Small variations in the bias, due to the discharge of capacitor, have no effect on the output voltage, which remains zero during this period of conductivity. When the neon tube 3 is nonconducting, the cutoff bias is removed so that a constant plate current flows. This amplfier then operates only on the self bias across resistor 5 due to the cathode current through it. The maximum voltage obtainable is therefore constant throughout this portion of the cycle. Its value is, of course, de-

voltages corresponding to those obtained in Figs.

3 and 4.

I have therefore illustrated an oscillator having a wave shape which may be rectangular, or substantially so. This oscillator is extremely simple to construct, reliable in operation, and adaptable to a widely varying range of rectangular wave shape.

I claim as my invention:

1. In a rectangular wave generator of the character described, the combination of a gas tube oscillator which includes a capacitor, a, first resistor connetced across said capacitor, a pair of two-electrode gaseous discharge tubes whose breakdown and current conduction is dependent upon the potential diiference impressed between said two electrodes, connections from one electrode of each of said tubes to respective terminals of said capacitor, a source of substantially constant d-c potential connected between a selected point intermediate the ends of said resistor and the remaining electrode of one of said tubes, whereby said tubes alternately and intermittently conduct current, a second resistor connected between the remaining electrode of the other of said tubes and said source for deriving a voltage from periodic current through said other of said tubes, and an amplifier tube having cathode, grid and anode electrodes, direct connections from said cathode and said grid to spaced points, respectively, on said second resistor for deriving therefrom a bias voltage from the intermittent current flow through said other of said discharge tubes of sufflcient value to bias said amplifier to plate current cut-oil, and a third resistor connecting said anode to said source of d-c potential for deriving a substantially rectangular voltage wave whose amplitude is determined by said amplifier and whose time interval and frequency is determined by said oscillator.

2. Ida rectangular wave generator, a pair of gaseous discharge tubes having two electrodes, 9. source of substantially constant direct voltage connected to said tubes for causing said tubes to break down and become current conductive, means occasioned by the break-down of each of said tubes for reducing the direct voltage applied to the other of said tubes to thereby delay breakdown of said other of said tubes, whereby said tubes alternately and intermitently become conductive, resistance means directly'connected in series circuit with said source and one of said gaseous discharge tubes for developing in said resistance means a voltage from and proportional to the current through said one of said gaseous discharge tubes, and means for modifying the characteristic of said voltage comprising an amplifier tube having a cathode, grid and anode electroeds, said source being connected in' a series circuit between said anode and cathode electrodes, said resistance means being connected in said series circuit between said source and said cathode, said grid electrode being connected to said resistance means at a point remote from said cathode for deriving a voltage drop of sufficient value to bias said amplifier tube to plate current cut-oi! when said one of said gaseous discharge tubes breaks down and is conducting.

3. The combinationin a rectangular wave generator, of an amplifier having anode, grid and cathode electrodes; a source of direct current voltage connected in a series circuit between said anode and cathode electrodes; a self-bias resistor connected in said series circuit between said source and said cathode; output circuit means connected in said series circuit between said anode and said source; said grid being connected to a point on said bias resistor remote from said cathode to derive therefrom a self-bias potential, whereby a substantially constant voltage is developed in said output means of a value determined by said self-bias potential, the plate ill voltage, and the plat circuit impedance; and a gas tube oscillator circuit comprising a gaseous discharge tube and said self-bias resistor connected in series with means causing intermittent breakdown of said tube and the flow of gaseous conduction current through said self-bias resistor for biasing said amplifier to plate current cut-ofi during the time of said breakdown.

GILBERT SWIFT. 

